1. Field of the Invention
The present invention relates to a method for manufacturing semiconductor devices including MOS (metal oxide semiconductor) transistor using electrons or holes as carrier, and especially, relates to a method for etching a sample, capable of performing etching with stabilized processing profile even after the occurrence of an idling in which mass production etching process is temporarily discontinued.
2. Description of the Related Art
Along with the recent improvement in integration and speed of semiconductor integrated circuits, there are demands to further enhance the miniaturization of gate electrodes. However, since a slight change in the dimension of gate electrodes causes the source/drain current and the leak current during stand-by to be varied greatly, it is extremely important to stabilize the accuracy of dimension (CD: critical dimension) of gate electrodes and to stabilize the processing profile thereof.
The change of radical status in the plasma within the etching reactor that affects the processing profile is mainly caused by the following two causes.
The first cause is the physical adhesion of reaction products on the uppermost surface of the reactor or the chemical change of the uppermost surface of the reactor through etching. In that case, even if plasma is generated via the same conditions, the consumption quantity of radicals and the recombination probability of radicals on the uppermost surface of the reactor are changed, and thus, the radical density in the plasma is changed.
The second cause is the change in the uppermost surface temperature of the reactor material. In that case, since the adsorption coefficient and the reaction speed of etching radicals, depositing radicals and reaction products on the uppermost surface of the reactor vary, the speed in which the uppermost surface of the reactor material is etched and the deposition speed thereof are varied. As a result, the balance of radicals and reaction products being consumed in the uppermost surface of the reactor is changed, and thus, the radical density in the plasma is changed.
In other words, in order to maintain a stable processing profile, it is important to (1) maintain a constant physicochemical status of the uppermost surface of the reactor, and (2) maintain a constant uppermost surface temperature of the reactor material. However, in the field of actual semiconductor mass production using etching apparatuses, there are cases where the physicochemical state of the uppermost surface of the reactor is changed, and mass production processing is temporarily discontinued.
In the prior art, with respect to the above-mentioned cause (1), the physicochemical status of the uppermost surface of the reactor is maintained for example by removing reaction products via cleaning or by coating the surface using carbon-based deposition gases. Published Japanese translation of PCT international publication No. 2003-518328 (patent document 1) discloses performing in-situ cleaning of reaction products, and then depositing a carbon-based coating so as to stabilize the processing profile.
With respect to the above-mentioned cause (2), Japanese patent application laid-open publication No. 2005-244065 (patent document 2) discloses a method for maintaining the temperature of the uppermost surface of the reactor by generating plasma using a processing condition set in advance based on plasma processing history so as to control the uppermost surface temperature of the reactor and stabilize the processing profile.
According to the apparatus disclosed in patent document 1, it is possible to remove the reaction products deposited in the processing chamber, but with respect to the second cause (2), it is not possible to stabilize the processing profile. Further, the apparatus disclosed in patent document 2 is capable of coping with the above-mentioned causes (1) and (2), but it is necessary to either attach a temperature measuring device to the apparatus before starting mass production to measure the temperature off-line, or perform simulation. The attachment of a temperature measuring device cannot be performed easily, since not only is it time-consuming to attach the device, but it may also cause metal contamination and generate particles. Further, according to heating techniques referring to an off-line temperature database or to temperature prediction via simulation, the data regarding the uppermost surface of the reactor is not monitored in real time, so there is a limit in the accuracy of reproduction of the processing profile after idling. In other words, the disclosure of patent document 2 offers only limited response to causes (1) and (2).